Perforating gun assembly to control wellbore fluid dynamics

ABSTRACT

A downhole tool used in the pressure isolation of adjacent subterranean formations. The downhole tool may comprise flow restriction devices along the outer circumference for impeding flow along the length of the tool. The tool may further comprise a perforating gun and an accumulator. Impeding flow along the length of the tool provides a dynamic flow restriction within the wellbore that precludes fluid flowing from one subterranean zone to an adjacent zone.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of and claims priority to andthe benefit of co-pending U.S. application Ser. No. 11/602,107, filedNovember 20^(th), 2006, the full disclosure of which is herebyincorporated by reference herein in its entirety for all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of oil and gas production.More specifically, the present invention relates to a perforatingsystem. Yet more specifically, the present invention relates to aperforating gun system capable of regulating wellbore fluid dynamics.

2. Description of Related Art

Perforating systems are used for the purpose, among others, of makinghydraulic communication passages, called perforations, in wellboresdrilled through earth formations so that predetermined zones of theearth formations can be hydraulically connected to the wellbore.Perforations are needed because wellbores are typically completed bycoaxially inserting a pipe or casing into the wellbore. The casing isretained in the wellbore by pumping cement into the annular spacebetween the wellbore and the casing. The cemented casing is provided inthe wellbore for the specific purpose of hydraulically isolating fromeach other the various earth formations penetrated by the wellbore.

Perforating systems typically comprise one or more perforating gunsstrung together, these strings of guns can sometimes surpass a thousandfeet of perforating length. In FIG. 1 an example of a perforating system4 is shown. For the sake of clarity, the system 4 depicted comprises asingle perforating gun 6 instead of a multitude of guns. The gun 6 isshown disposed within a wellbore 1 on a wireline 5. The perforatingsystem 4 as shown also includes a service truck 7 on the surface 9,where in addition to providing a raising and lowering means, thewireline 5 also provides communication and control connectivity betweenthe truck 7 and the perforating gun 6. As is known, derricks, slips andother similar systems may be used for inserting and retrieving theperforating system into and from a wellbore. Moreover, perforatingsystems may also be disposed into a wellbore via tubing, drill pipe,slick line, coiled tubing, to mention a few.

Included with the perforating gun 6 are shaped charges 8 that typicallyinclude a housing, a liner, and a quantity of high explosive insertedbetween the liner and the housing. When the high explosive is detonated,the force of the detonation collapses the liner and ejects it from oneend of the charge 8 at very high velocity in a pattern called a “jet”12. The jet 12 perforates the casing and the cement and creates aperforation 10 that extends into the surrounding formation 2.

As shown in FIG. 2, subsequent to the perforating step, formation fluidflows from the formation 2, into the wellbore 1, and through the annulus11 formed by the outer circumference of the perforating gun 6 and theinner diameter of the wellbore 1 (the direction of this fluid flow isillustrated by arrows A). Fluid flows from the formation 2 into thewellbore 1 because the wellbore pressure is exceeded by the formationpressure, this is commonly referred to as an under-balanced situation.Debris 14 from the formation however often travels along with the fluid,this debris 14 can sometimes collect within the annulus 11 and incertain locations thereby resulting in a clog 16 that can effectivelylodge the perforating gun 6 within the wellbore 1. The connate fluid isshown flowing from within a first zone Z₁, into the wellbore Tinto zoneZ₂. This presents a problem if it is desired to maintain these separatezones Z₁, Z₂ at separate pressures.

BRIEF SUMMARY OF THE INVENTION

The present disclosure discloses examples of a perforating system and amethod of perforating. In an example embodiment a perforating system ismade up of a perforating string with first and second spaced apartperforating guns. Shaped charges are provided in both guns and a zonalisolation system is included for regulating pressure in a wellbore. Thezonal isolation system of this embodiment has axially spaced apartplates that project radially out from the perforating string. The platesdefine an annulus between the string and a borehole wall, where theannulus restricts fluid flow to cause a pressure drop in the fluidflowing across the plates and along the annular space between theperforating string and wall of the wellbore. This lowers pressure in afluid flowing from a higher pressure producing zone so that it does notflow into a lower pressure producing zone. In an example embodiment,passages are formed through the plates. Optionally, the diameters of theplates can vary. The zonal isolation system may be disposed on one ofthe first or second perforating guns. In an example embodiment, thezonal isolation system is disposed between the first and secondperforating guns. A sub may optionally be included that connects betweenthe first and second perforating guns. In this example the zonalisolation system is disposed on the sub. In an example embodiment, thezonal isolation system is a first zonal isolation system, and a secondzonal isolation system is included with the system.

Also disclosed herein is an alternate perforating system that has aperforating string with shaped charges. The perforating string has astack of axially spaced apart plates projecting radially outwardtherefrom that define a restricted flow area between a portion of theperforating string and a wellbore wall. As such, when shaped charges inthe perforating string are detonated and perforate formation zonesadjacent the wellbore, if the formation zones are at differentpressures, fluid communication between the respective formations isimpeded by the plates. In an example embodiment, the perforating stringincludes perforating guns stacked end to end. Optionally, the platesdirect fluid from one of the formations along a labyrinthine path forreducing pressure in the fluid. Passages may optionally be included thatare formed axially through the plates. Further, the passages in adjacentplates may be offset from one another. Yet further optionally, thediameters of the plates can vary.

A method is described herein for dynamically isolating flow within awellbore between a first subterranean formation zone and a secondsubterranean formation zone, where the zones are at different pressures.In an example the method includes inserting a downhole tool in awellbore, where the downhole tool includes a pressure isolation systemthat has axially spaced apart plates that extend radially outward froman outer surface of the downhole tool. A restricted flow annulus isdefined between the member and the wellbore. Connate fluid flow isinduced from within the first and second subterranean formation zonesand a dynamic pressure drop is created between the first and secondsubterranean formation zones by locating the restricted flow annulusbetween the first and second subterranean formation zones. Directingconnate fluid from the higher pressure formation across the restrictedflow annulus reduces pressure in the fluid to prevent the fluid fromflowing into the lower pressure formation zone. In an exampleembodiment, the plates are configured to form a labyrinthine path forconnate fluid flow along the downhole tool. Alternatively, thelabyrinthine path is formed by providing passages through the plates andpositioning the passages in each plate to be axially offset frompassages in an adjacent plate. Yet further alternatively, thelabyrinthine path is formed by varying the diameter of plates that areadjacent.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

Some of the features and benefits of the present invention having beenstated, others will become apparent as the description proceeds whentaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a partial cutaway side view of a prior art perforatingoperation.

FIG. 2 is a partial cutaway side view of a prior art perforatingoperation with formation fluid flowing into a wellbore.

FIG. 3 is a side partial sectional view of a perforating string inaccordance with the present disclosure.

FIG. 4 is a side partial sectional view of a perforating string in adeviated wellbore and in accordance with the present disclosure.

FIG. 5 is a side partial sectional view of an embodiment of a downholetool disposed in a wellbore in accordance with the present disclosure.

FIG. 6 is a partial cut-away side view of a downhole tool disposed in adeviated wellbore in accordance with the present disclosure.

FIG. 7 is a side partial sectional view of an alternate embodiment of aperforating string for regulating wellbore pressure in accordance withthe present disclosure.

FIG. 8A is a side perspective view of a portion of the perforatingstring of FIG. 7 that includes an alternate embodiment of a restrictionplate.

FIG. 8B is a side perspective view of a portion of the perforatingstring of FIG. 7 that includes an alternate embodiment of a restrictionplate.

While the invention will be described in connection with the preferredembodiments, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications, and equivalents, as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE INVENTION

The method and system of the present disclosure will now be describedmore fully hereinafter with reference to the accompanying drawings inwhich embodiments are shown. The method and system of the presentdisclosure may be in many different forms and should not be construed aslimited to the illustrated embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey its scope to those skilled in the art.Like numbers refer to like elements throughout.

It is to be further understood that the scope of the present disclosureis not limited to the exact details of construction, operation, exactmaterials, or embodiments shown and described, as modifications andequivalents will be apparent to one skilled in the art. In the drawingsand specification, there have been disclosed illustrative embodimentsand, although specific terms are employed, they are used in a genericand descriptive sense only and not for the purpose of limitation.Accordingly, the improvements herein described are therefore to belimited only by the scope of the appended claims.

With reference now to FIG. 3 an embodiment of a perforating system 20 inaccordance with the present disclosure is illustrated in a side view.The perforating string 20 of FIG. 3 includes a perforating section 22axially connected to an accumulator section 26. As shown, anotherperforating section 23 is connected on the end of the accumulatorsection 26 opposite the perforating section 22. It should be pointed outthat the number of perforating sections (or guns) is not limited to thenumber shown but could be any number of guns included with theperforating string 20 of the present disclosure.

An auger flight 28 is provided along the outer circumference of theperforating string 20. The auger flight 28 is a generally helical memberthat winds along on the outer circumference of the perforating string 20along a portion of its length. As shown, the auger flight 28 is disposedprimarily along the accumulator section 26 of the perforating string 20.Optionally the auger flight 28 may extend also along one or more of theperforating sections 22, 23 in addition to being along the accumulatorsection 26. It should be pointed out that the cross section of the augerflight 28 may take one of many different configurations. Typically thebase of the auger flight 28 has a wider cross section where it attachesto the perforating string 20 and tapers to a narrower cross section atits outer edge. Other embodiments of the auger flight 28 include a shapewhere the base and the terminating end have substantially the samethickness with no tapering. However it is well within the scope of thoseskilled in the art to determine and produce an auger flight suitable foruse.

A port 30 is provided on the accumulator section 26 that may beselectively opened or closed. When open, the port 30 provides fluidcommunication across the side walls of the perforating string 20.Optionally, a reservoir 30 (shown in dashed lines) can be providedwithin the perforating string 20 and in communication with the port 30.Opening/closing of the port 30 may selectively communicate fluid betweenthe reservoir 30 and outside of the perforating string 20. The reservoir32 can be disposed solely within the accumulator section 26 or one ofthe perforation sections 22, 23.

In one non-limiting example of operation, a perforating system 4 havingan embodiment of the perforating string 20 herein described is loweredwithin a wellbore 1 to a predetermined depth wherein perforatingoperations are to be performed. Initiating detonation of shaped charges24 shown provided with the perforating system 4 creates perforations 10in the corresponding formation 2. As previously discussed, in anunder-balanced situation, fluid in the higher pressure formation 2 willflow into the lower pressure wellbore 1 through the perforations 10. Theports 30 can be opened, simultaneously with initiation of the shapecharges 24 or soon thereafter, so the reservoir 32 can act as apotential sink or accumulator for at least a portion of the formationfluid flowing into the wellbore 1 from the formation 2. The fluidflowing into the reservoir 32 is not limited to wellbore fluid but canalso include all flowable matter resident in the wellbore 1, such asdrilling mud, drilling fluid, as well as the producing fluid from theformation 2. Accordingly having the accumulator section 26 within thewellbore 1 after perforating provides an open space to absorb potentialkinetic energy resulting from the pressure imbalance between theformation 2 and the wellbore 1.

Pressure imbalances between the formation 2 and the wellbore 1 mayresult from changes in the density of fluid in the wellbore, or byperforating into a formation 2 having a higher pressure than thewellbore 1. Flow into the wellbore 1 from the formation 2 may be inducedby perforating into a formation 2 as well as introducing an accumulatorwithin a wellbore 1 having wellbore fluid, wherein the confines of theaccumulator are at a lower pressure than the wellbore fluid. Providingfluid communication between the confines of the accumulator and thewellbore 1 can also induce connate fluid flow from the formation 2 intothe wellbore 1. As discussed in more detail below, the accumulator incombination with the auger flights can isolate the pressure of onesubterranean zone from another.

With reference now to FIG. 4, an additional embodiment of the device ofthe present disclosure is shown disposed within a deviated portion of awellbore 1 a. In this situation the wellbore 1 a is shown intersectingdifferent zones Z₁, Z₂, Z₃, within a formation 2 a. Although theembodiment of FIG. 4 is disposed within a deviated portion of thewellbore la, the embodiment shown is operable within wellbore sectionsthat are substantially vertical and/or horizontal. In thisconfiguration, the perforating sections 22 a, 23 a are proximate todifferent zones Z₁, Z₃ within the formation 2 a. This can be significantwhen the resident pressure of either Z₁ or Z₃ is sufficiently greater orless than the other zone such that upon perforation the fluid of onezone empties fluid into the wellbore 1 a with a sufficiently higherpressure that the fluid back flows into the lower pressure zone. Theadvantages of the device described herein alleviate such a back flowcondition due to its flow restriction and pressure absorptioncapabilities, i.e. the auger flight 28 and reservoir 32. The augerflight 28 restricts flow by reducing the cross sectional area availablefor fluid flow thereby causing dynamic pressure losses. The reservoir32, by virtue of fluid communication of the ports 30, can absorb energystored in the fluid as pressure thereby further preventing against sucha back flow condition. Accordingly, the present device maintains a fluidpressure differential between subterranean zones Z₁, Z₂, Z₃ to zonalisolate the zones Z₁, Z₂, Z₃. The zonal isolation, which typicallyoccurs dynamically (dynamic zonal isolation), can be accomplished by theadded pressure surge capabilities of the accumulator section, thepressure drop function of the auger flight, as well as a combination ofthese two.

The scope of the present disclosure is not limited to perforatingsystems, but as shown in FIG. 5, can include any tool 38 disposablewithin a wellbore, such as those used in removing debris from withinexisting perforations (commonly referred to as a downhole surgeassembly). The embodiment of the tool 38 of FIG. 5 includes a flowrestrictor section 40 for retarding flow across the length of the tool.The flow restrictor section 40 can include surface elements, such as anauger flight 42, a series of orifice plates 44, some other member forretarding flow, or a combination thereof. Although the flow restrictorsection 40 shown in FIG. 5 includes more than one type of member forrestricting flow, a single member type may be used on the tool 38 forrestricting flow. The flow restrictor section 40 thus may comprise anymember (flow restriction member) that restricts or otherwise impedesfluid flow axially through the wellbore 1. Optionally, an accumulator 46(shown as a dashed line) may be included within the tool 38 formed toreceive fluid flow therein. Ports 48 may be provided as shown to enablefluid flow from within the wellbore 1 into the accumulator 46. Whileoperation of the device of FIG. 5 may not include perforating, the tool38 could be inserted post perforation. The tool 38 as shown could beused to create an underbalanced condition within a wellbore for coaxingconnate fluid 52 from a formation Z₁ into the wellbore 1. By flowingfluid from the formation Z₁ into the wellbore, perforations 50, 54opening formation Z₁, Z₃ to the wellbore 1 can be cleaned free of anydebris that may have accumulated while perforating or thereafter. Theflow restrictor section 40 impedes fluids axially flowing through thewellbore 1. As discussed above, the flow restrictor and the fluidaccumulator, either separately or in combination, impede fluid flow byreducing the available cross sectional area available for flow (in thecase of the flow restrictor) or by absorbing fluid potential energy (byusing an accumulator). Impeding fluid flow through the wellbore 1provides dynamic zonal isolation along the body of the tool 38 therebyisolating subterranean zones from one another. As discussed above, thezonal isolation provided by the tool 38 prevents fluid communicationbetween the zones.

Optionally the present device may further allow pressure isolationbetween various subterranean zones Z₁, Z₂, Z₃. For example, as shown inFIG. 6 an embodiment of a downhole tool 70 disposed in a wellbore 71,wherein the wellbore 71 extends through multiple zones Z₁, Z₂, Z₃ havingdiffering physical and/or pressure properties. The downhole tool 70 isshown equipped with isolation elements 72, that in one example can be anauger flight as described above, disposed at strategic points along itsouter surface. The isolation elements 72 include any device extendingoutward from the surface of the downhole tool 70 for impeding fluid flowin the annulus formed between the inner circumference of the wellbore 71and the outer circumference of the downhole tool 70. Examples ofdownhole tools 70 considered include perforating guns (with or withoutaccumulator sections) and perforation surge assemblies. Additionally,the downhole tool 70 could comprise a series of surge assemblies 77, 79,81 configured to accommodate a particular zone. Optional ports 83 thatare selectively opened are shown included to flood the assemblies. Thestrategic points may correspond to boundaries 74, 75 between zones Z₁,Z₂, Z₃ that are adjacent. Thus strategic placement of the downhole tool70 within the wellbore 71 may control and manipulate pressure surgesbetween adjacent zones via the wellbore 71. The presence of theisolation elements 72 serves to impede fluid flow through the wellbore71 along the downhole tool 70. Impeding fluid flow in this manner inturn regulates pressure communication between different zones to zonallyisolate these zones Z₁, Z₂, Z₃.

Referring now to FIG. 7, an example embodiment of a perforating string20B is illustrated deployed in the wellbore 1; where a wellhead assembly76 is mounted at the entrance to the wellbore 1. A deployment means 77,which can be a wireline, slickline, coiled tubing, or the like, suspendsthe perforating string 20B downhole. Shaped charges 24 in theperforating string 20B are shown being detonated to create jets 78 thatpenetrate the formation 2 adjacent the wellbore 1. Initiating the shapedcharges 24 may occur from a detonation signal delivered through thedeployment means 77. Perforations 50, 80 are created in zones Z₁, Z₂ inthe formation 2. Flow restrictor sections 40A are shown provided on theouter circumference of the perforating string 20B. In the embodiment ofFIG. 7, the flow restrictor sections 40A include a stack of axiallyspaced apart plates 81 that circumscribe a body of a perforating gun 82of the perforating string 20B and a sub 84 attached on an upper end ofthe gun body 82. The sub 84 can be a connector sub for connectingperforating guns 82 in the perforating string 20B, an accumulator sub asdiscussed above, or a sub or tool having a different function.

Embodiments of the plates 81 of FIG. 7 include a washer like elementhaving an inner diameter substantially the same as the outer diameter ofthe portion of the perforating string 20B of where the plate 81 ismounted. An outer diameter of the plates 81 may extend up to the innerdiameter of the wellbore 1. Examples of ratios of thickness (or height)to diameter of the plates 81 range from about 1:5 to about 1:30. Theouter periphery of the plates 81 is generally circular, but may havedifferent shapes to match the inner surface of the wellbore 1. A gapexists between the outer diameter of the plates 82 and inner surface ofthe wellbore 1 to define an annulus 86. As discussed above, the plates82 reduce the area between the perforating string 20B and walls of thewellbore 1 thereby creating a restriction to flow that in turn increasesa pressure drop to fluids flowing across the restriction to preventfluid from a higher pressure to a lower pressure zone Z₁, Z₂.

Shown in a side perspective view in FIG. 8A is a section of theperforating gun 82 or sub 84 of FIG. 7 having an alternate embodiment ofthe plates 81A that include passages 88 formed through the plates 81A.In this example embodiment, the plates 81A may have a larger diameterthereby urging more fluid radially inward to force the fluid through thepassages 88. Further, by staggering the positioning of the passages 88within adjacent plates 81A, the flow of fluid, as represented by arrows,may follow a labyrinth like path. Pressure in the fluid is lost as thefluid flows through each passage 88 as well as flowing along the longerlabyrinthine path. FIG. 8B also illustrates an alternate embodiment ofisolating one formation zone Z₁, Z₂ from another. In the example of FIG.8B, plates 81B have an outer diameter less than other plates 81 on theperforating gun 82 or sub 84. The varying outer diameters of the plates81, 81B can induce formation of eddy currents in the flow of fluid thatcan further induce pressure losses in the fluid flow. Optionally, theembodiments of FIGS. 8A and 8B may be combined so that plates of varyingdimensions include passages therethrough.

The embodiments described herein, therefore, are well adapted to carryout the objects and attain the ends and advantages mentioned, as well asothers inherent therein. While a presently preferred embodiment of aninvention has been given for purposes of disclosure, numerous changesexist in the details of procedures for accomplishing the desiredresults. For example, instead of an auger flight extending partiallybetween the outer surface of a downhole tool and the inner surface of acasing, other flow path restriction members may be employed. Examples ofsuch members include coaxially disposed plates, plates having orificestherethrough, a partially extended packer, as well as any other memberfor retarding flow across the length of the tool. Further, the downholeconveyance means used for disposing the above described devices includescasing and drill pipe. These and other similar modifications willreadily suggest themselves to those skilled in the art, and are intendedto be encompassed within the spirit of the present invention disclosedherein and the scope of the appended claims.

1. A perforating system comprising: a perforating string; first andsecond perforating guns that are spaced apart within the perforationstring; shaped charges in each of the first and second guns; and a zonalisolation system comprising plates that are axially spaced apart andproject radially outward from an outer surface of and around theperforating string for restricting fluid flow in an annular spacebetween the member and a borehole wall and causes a pressure drop in thefluid flow in the annular space so that the pressure in a fluid flowingfrom a higher pressure producing zone is reduced in the annular spaceand does not flow into a lower pressure producing zone.
 2. Theperforating system of claim 1, further comprising passages formedthrough the plates.
 3. The perforating system of claim 1, wherein thediameters of the plates vary.
 4. The perforating system of claim 1,wherein the zonal isolation system is disposed on one of the first orsecond perforating guns.
 5. The perforating system of claim 1, whereinthe zonal isolation system is disposed between the first and secondperforating guns.
 6. The perforating system of claim 1, furthercomprising a sub connected between the first and second perforatingguns, wherein the zonal isolation system is disposed on the sub.
 7. Theperforating system of claim 1, wherein the zonal isolation systemcomprises a first zonal isolation system, the perforating system furthercomprising a second zonal isolation system.
 8. A perforating systemcomprising: a. a perforating string; b. shaped charges in theperforating string; c. a stack of axially spaced apart plates thatextend radially outward from the perforating string to define arestricted flow area between a portion of the perforating string and awellbore wall when the perforating string is in a wellbore, so that whenshaped charges in the perforating string are detonated and formperforations into formation zones adjacent the wellbore and havingdifferent pressures, fluid communication between the respectiveformations is impeded by the plates.
 9. The perforating system of claim8, wherein the perforating string includes perforating guns stacked endto end.
 10. The perforating system of claim 8, wherein the plates arefor directing fluid from one of the formations along a labyrinthine pathfor reducing pressure in the fluid.
 11. The perforating system of claim8, further passages formed axially through the plates.
 12. Theperforating system of claim 11, wherein the passages in adjacent platesare offset from one another.
 13. The perforating system of claim 8,wherein diameters of the plates varies.
 14. A method of dynamicallyisolating flow within a wellbore between a first subterranean formationzone and a second subterranean formation zone that is at a differentpressure than the first subterranean formation zone, the methodcomprising: a. providing a downhole tool in a wellbore that comprises anouter surface, and a pressure isolation system that has axially spacedapart plates that extend radially outward from the outer surface of thedownhole tool to define a restricted flow annulus between the member andthe wellbore, b. inducing connate fluid flow from within the firstsubterranean formation zone; c. inducing connate fluid flow from withinthe second subterranean formation zone; and d. dynamically creating apressure drop between the first and second subterranean formation zonesof different pressures by locating the restricted flow annulus betweenthe first and second subterranean formation zones and reducing pressurein the connate fluid from the subterranean formation zone having ahigher pressure, so that flow from the subterranean formation zonehaving the higher pressure does not flow into the other subterraneanformation zone.
 15. The method of claim 14, wherein the plates areconfigured to form a labyrinthine path for connate fluid flow along thedownhole tool.
 16. The method of claim 15, wherein the labyrinthine pathis formed by providing passages through the plates and positioning thepassages in each plate to be axially offset from passages in an adjacentplate.
 17. The method of claim 15, wherein the labyrinthine path isformed by varying the diameter of plates that are adjacent.